Genetic Association between Grain Yield of Bread Wheat and Carbon Isotope Discrimination under Drought in Morocco

The capacity of the wheat plant to discriminate against the carbon-13 isotope during photosynthesis, in favor of the lighter carbon-12 isotope, has been found to correlate with grain yield in many studies. This hypothesis was tested under four contrasting environments in Morocco during 2003-2006 using three sets of elite wheat genotypes. Significant positive correlations were found between carbon isotope discrimination (CID, Δ13C or Δ) and grain yield, and were higher under more water stressed environments at Douyet and Jemaa Sahim, indicating that high Δ is associated with high yield under drought stress. Selection based on yield appeared to have indirectly acted on Δ as well, since the correlation was significant and remained relatively unchanged across years of selection. This indicates a possible genetic linkage between yield and Δ. Also, transgressive segregation occurred for most agronomic and physiological traits, including Δ, offering a potential genetic variation for selection. At the molecular level, CID was found to be linked to a molecular marker at the gwm095 region of chromosome 2A, and to a thousand kernel weight marker at the gwm071 region, distant by 20-30 cent Morgan (cM). A poor QTL associated with grain yield was detected at chromosome 5A, similar to the one detected at CIMMYT in Obregon (Mexico) and northern Australia. From these results, it can be concluded that CID may be used as a new selection criterion to enhance wheat grain yield potential under drought in Morocco. (author)